Known devices for measuring the wavelength of optical signals, such as spectrometers, typically contain a combination of optical, mechanical, and electronic components. The spectral operational sensitivity of these components to changes in environmental conditions, such as temperature or ionizing radiation, necessitates calibration to ensure measurement accuracy. One type of calibration reference known in the art is a cell filled with a gas having narrowband molecular absorption lines being known wavelengths. When a broadband light source is used in connection with the gas cell to see the narrowband absorption lines, spectrometers may be used to distinguish between narrowband absorption lines of the gas cell for calibration purposes. Spectral monitor arrays, acousto-optic tunable filters (AOTFs), and monochromatic light sources have also been used for calibration purposes.